1. Field of Invention
The present invention relates to a phosphor. More particularly, the present invention relates to a fluorosulfide phosphor.
2. Description of Related Art
Light emitting diode (LED) is a kind of semiconductor light source. Comparing to transitional light sources, the characteristic of LEDs are small, luminescent efficiency, life-durable, energy saving and environmental friendly. Since LED has been used for illumination applications in recent years, much attention has been directed to develop white light emitting diode (WLED).
The most popular way to produce high intensity white LEDs are by phosphor method, i.e. phosphor-based LEDs. This method involves coating one color of an LED with different color of phosphors to form white light. There are two primary ways for producing white light based on the phosphor-based LEDs method. One is to encapsulate a near UV, purple or blue LED with a yellow phosphor to form white light; however this white light lacks of red and green of three primary colors, the white light displays in poor color rendering and cold colors temperature. The other is to encapsulate a near UV, purple or blue LED with red and green color phosphors, this kind of white light displays the warm color temperature and shows greater application ranges.
In recently years, Eu3+-doped oxide, Mn4+-doped fluoride, Eu2+-doped nitride, Eu3+-doped oxide, and Mn4+-doped fluoride are the most applied red phosphors coating in UV, near UV or blue light LEDs. Although Eu3+-doped oxide and Mn4+-doped fluoride phosphors display linear orange-red light, the color saturation of red light emitted from that two phosphors are still insufficient. Broad band emission of Eu2+-doped nitride are investigated, but the preparing condition of Eu2+-doped nitride are not feasible, since they must be calcined under high pressure and high temperature condition, resulting in increasing in producing cost.
Besides, yellow-green color emitting Eu2+-doped oxide and Tb3+-doped oxide compounds are the common green phosphors applied in UV, near UV or blue light LEDs. Tb3+-doped oxide compounds shows the less conversion efficiency for its linear yellow-green light in the blue light range. Although Eu2+-doped oxide compound display the broad band emitting range, the highly hygroscopic quality of this compound making it difficult to save and higher cost.